1. Field of the Invention
The present invention relates to devices and installations for the burning and/or sintering and subsequent cooling of cement clinker, lime, magnesite, dolomite, and similar materials, such as iron ore pellets or lightweight filler materials (expanded clay) and, more particularly, to a small-scale cement mill or lime mill.
2. Description of the Prior Art
Among known installations of the above-described type are the so-called multi-level shaft kilns which have a charging shaft into which the raw granulate or crushed rock is fed from above, and inside which the latter is dried and preheated. At its lower end, the shaft opens into a burn chamber inside which is arranged a movable platform supporting the charge. The latter forms a slope whose exterior layer is periodically discharged over the forward edge of the platform, as the platform is retracted, the treated materials falling into a cooling shaft. These installations are equipped with various blowers for the introduction and removal of hot gases and cold air. Shaft kilns of this type are disclosed in German Offenlegungsschrift No. 2,312,379 and No. 2,434,852.
In comparison with rotary kilns, the multi-level shaft kilns have the advantage that both their construction costs and their operating costs are lower.
In such a multi-level shaft kiln, the burning or sintering process takes place inside a burn chamber in which the slope of the dried and preheated raw granulate is exposed to the hot combustion gases produced by a burner unit. The result is something of a combined burning and sintering process. While the granulate is being calcined in the upper portion of the material slope, it is being sintered in the lower portion of the slope, for example. However, the exact place where calcining stops and sintering starts cannot be determined and controlled, as the two processes depend from a multitude of parameters.
Attempts to better control the changing conditions which determine the burning process and the sintering process have already led to the development of shaft kilns of the so-called double-slope type and of hearth kilns which have staggered superposed multiple hearths, using several burn chambers. Such a kiln is shown in German Auslegeschrift No. 1,558,076. These special kilns, however, do not produce a controlled material flow. While they offer an improved controllability of the burning process and sintering process, they have the additional shortcoming that their construction is considerably more complex and costly, limiting their applicability to very large installations of elevated construction cost.